title: Disclosing an NMR-invisible fraction in chitosan and PEGylated copolymers and its role on the determination of degrees of substitution.
abstract: An unexpected (1)H NMR invisible fraction (IF) for chitosan (CS) and CS-g-PEG is reported. The presence of this IF is remarkable considering that solution NMR is recognized as the method of choice for studying structural modifications in CS, including the degrees of acetylation (DA) and substitution (DS). In spite of IF figures as high as 50%, this IF does not interfere in the correct determination of the DA by (1)H NMR, pointing to a homogeneous distribution of acetyl groups along the visible and invisible fractions. Quite in contrast, the IF negatively biases the determination of the DS in CS-g-PEG, with relative errors as high as 150% in a broad range of temperatures, pH values, and concentrations. This fact raises concerns about the accuracy of previously reported DS data for CS-g-PEG and many other CS copolymers. Efficient user-friendly conditions have been developed for the correct determination of the DS of CS-g-PEG by depolymerization by nitrous acid.
authors.affiliation: Department of Organic Chemistry and Center for Research in Biological Chemistry and Molecular Materials (CIQUS), University of Santiago de Compostela , Jenaro de la Fuente s/n, 15782 Santiago de Compostela, Spain.
authors.forename: Ramon
authors.initials: R
authors.lastname: Novoa-Carballal
authors.forename: Ricardo
authors.initials: R
authors.lastname: Riguera
authors.forename: Eduardo
authors.initials: E
authors.lastname: Fernandez-Megia
mesh_terms: D048271:Chitosan / Q000737:chemistry*; D008279:Magnetic Resonance Imaging; D011092:Polyethylene Glycols / Q000737:chemistry*; D011108:Polymers / Q000737:chemistry*
chemical_list: D011108:Polymers; D011092:Polyethylene Glycols; D048271:Chitosan